Engine starters, which are also commonly referred to as “starter motors” or simply “starters”, are used to crank vehicle engines. Most engine starters include an electric motor that is coupled to an internal gear train or other gear assembly. The gear assembly transfers rotation of the electric motor to a pinion gear of the engine starter. Exemplary gear assemblies include planetary gear arrangements connected to an output shaft of the electric motor. An overrun clutch is typically connected between the gear assembly and the pinion gear. A solenoid arrangement is configured to move the pinion gear between an engaged position where the pinion is meshed with the engine ring gear and a disengaged position where the pinion is removed from the engine ring gear.
To start an engine with the typical engine starter, the pinion gear is moved to the engaged position, in which the pinion gear becomes engaged with the engine flywheel via the ring gear. Next, the electric motor is fully energized, causing the pinion gear and the flywheel to rotate. The rotating flywheel puts the engine pistons into motion, which typically causes the engine to start. When the engine does start, the flywheel begins to rotate at a rate that is greater than that of the pinion gear, and the overrun clutch decouples the pinion gear from the output of the gear train. This prevents damage to the gear train, which may occur as a result of the rapidly rotating flywheel. The pinion gear is moved to the disengaged position after the engine is started.
When the pinion gear is engaged with the flywheel and is rotating the flywheel, the gear assembly and pinion gear of the engine starter experiences a pulsating torque resulting from moving engine parts, including piston movement within the engine cylinders. This pulsating torque is typically less than the stall torque (i.e., a magnitude of torque that causes the output shaft of the electric motor to stop rotating). However, the gear assembly may be loaded with a torque that is much greater in magnitude than the stall torque during certain engine events. These engine events may include engine backfire, hydraulic lock-up, a jammed pinion, or attempted engagement of the pinion gear with the flywheel after the engine is already started. The high torque is primarily caused by kinetic energy stored in the output shaft of the electric motor, which is then converted to strain energy upon rapid deceleration of the output shaft.
Vehicle manufacturers require that the engine starter should not fail or cause failure of other engine components as a result of the high-torque engine events such as those mentioned above. To meet this requirement, engine starter manufacturers design engine starter components to withstand a torque in excess of the stall torque. This often results in engine starter components being larger, heavier, or made from more robust and expensive materials than if the components were only required to withstand the torque encountered during normal engine operation. Additionally, many engine starters include torque limiters coupled to the gear assembly. These torque limiters are configured provide relief from excessive torque events preventing the pinion from being driven by the electric motor when a threshold torque is exceeded. Unfortunately, these torque limiters add unwanted additional size to the engine starter. Moreover, some torque limiters that have added only limited additional size to the engine starter have typically failed to accommodate sufficient torque capacity while also providing sufficient durability.
In view of the foregoing, it would be desirable to provide a torque limiter for an engine starter that is durable and accommodates large torque capacity. It would also be desirable for such torque limiter to add little or no additional size to the engine starter. Furthermore, it would be desirable for such torque limiter to be relatively easy and inexpensive to manufacture.